Contents lists available at ScienceDirect International Journal of Thermal Sciences journal homepage: www.elsevier.com/locate/ijts Prediction of local shear stress and heat transfer between internal rotating cylinder and longitudinal cavities on stationary cylinder with various shapes A. Nouri-Borujerdi * , M.E. Nakhchi School of Mechanical Engineering, Sharif University of Technology, Iran ARTICLE INFO Keywords: Simulation of annular flow Turbulent flow Heat transfer Cavities with trapezoidal cross section ABSTRACT A numerical analysis has been performed to simulate flow structure, heat transfer, and pressure drop of turbulent flow in an annulus with a few longitudinal cavities on the outer stationary cylinder. The cross sections of cavities are rectangular, closed and open trapezoidal shapes. This kind of annular flow is applicable to industries ap- plications such as electrical generators where heat generates in the cavities containing wires, heating of axial compressor rotor drams, rotating heat pipes for cooling of superconducting machines or motor rotor. The governing equations of turbulent flow are solved by using Renormalization group (RNG) k–ε model for Reynolds and Taylor numbers in the range of × < < × 5 10 Re 6.5 10 a 3 4 and < < Ta 160 1900 respectively. The angle between the sides and the base of the trapezoid cavity is in the range of < < ∘ ∘ β 70 135 . The results show that the pressure drop is dependent on the cavity angle and reaches a maximum value at = ∘ β 91 , then declines. Furthermore, Sharp increase in heat transfer coefficient belongs to the corners of the cavity where are located in front of the fluid rotational flow. Furthermore, the averaged Nusselt number is dependent on both the effective Reynolds number and the aspect ratio but the Reynolds number is more effective. The present results are va- lidated with available experimental data in the literature for rectangular cavities. 1. Introduction Fluid flow between two cylinders in the presence of rotational speed and axial velocity is called Taylor-Couette-Poiseuille flow. This type of flow is very popular in rotating heat pipes, gas cooled nuclear reactors, chemical mixers and electrical motors [1–3]. Heat transfer enhance- ment in rotating devices is one of the most important design factors. Therefore, to prevent overheating and failure the winding wire in- sulation of electric motors and generators cooling must be done well. Dirker and Meyer [4] conducted a comparative study of literature involving convection heat transfer in annulus. They concluded that more research is needed in the area of convective heat transfer corre- lations in concentric annulus, as little agreement is found among ex- isting correlations. Gnielinski [5] developed a correlation for turbulent heat transfer coefficient on the basis of a large number of experimental data from the literature. In his research, a proven correlation for heat transfer in circular tubes was extended by factors that take into con- sideration the effect of the diameter ratio of the annulus and the dif- ferent boundary conditions for heating or cooling. Lopez et al. [6] considered instabilities driven by the combination of rotation and thermal gradients. This instability determines the dynamics of complex geophysical, astrophysics and industrial flows. Ali and Weidman [7] performed a detailed linear stability analysis of such flows using axial periodicity and reported on the influence of the Prandtl number and on the stability boundaries. Their results showed a good agreement with the results of Snyder et al. [8] and, to a lesser extent with the results of Sorour and Coney [9]. Ali and Weidman attributed the discrepancies to the limitations of linear stability theory and the infinite-cylinder idea- lization to capture the experimental details. A similar linear stability analysis by Yoshikawa et al. [10] reported good agreement between numerical results and related results of Lepiller et al. [11]. Nonlinear simulations for small temperature gradients were provided by Ball and Farouk [12] who quantified the heat transfer across the system. Zhao et al. [13] numerically investigated the fully developed Taylor-Couette flow of a drilling fluid between two rotating cylinders. They concluded that the flow field is highly affected by the shear-thinning behavior of the drilling fluid between two cylinders. The effect of the inner cylinder movement on the heat transfer and melting of PCM of a double pipe heat exchanger was numerically investigated by Pahamli et al. [14]. The results show that inner pipe downward movement increases the convection heat transfer which reduces melting time up to 64%. Recently, cylindrical channels with longitudinal cavities on the surface are widely used for heat transfer enhancement due to higher fluid mixing [15–18]. The cavities disturb the incoming boundary layer https://doi.org/10.1016/j.ijthermalsci.2019.01.016 Received 31 March 2018; Received in revised form 18 November 2018; Accepted 14 January 2019 * Corresponding author. E-mail addresses: anouri@sharif.edu (A. Nouri-Borujerdi), erfanian@mech.sharif.ir (M.E. Nakhchi). International Journal of Thermal Sciences 138 (2019) 512–520 1290-0729/ © 2019 Elsevier Masson SAS. All rights reserved. T